What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Marantz 2385

Power Amplifier Section
High-Power Full Complementary Symmetry Output
The mammoth power of these Marantz receiver is generated by the most sophisticated full complementary output stages in use. Transistor array is  triple-paralleled in this 2385 - designs occasionally used separate components, but never before in receivers. They help provide long life, high power operation and exceptionally low Total Harmonic Distortion. As low, in fact, as that of the Marantz 510M professional power amplifier.
Also like the 510M, the Marantz 2385 are engineered to produce an extremely wide safe operating area - that range where voltage, current and temperature conditions permit reliable output stage operation. The amplifier sections are so stable, they will drive a load at virtually any frequency or level without breaking down.
In addition, the output stages of both receivers are biased for Class AB operation, a measure that prevents crossover distortion and ensures uncompromised performance to well below 1/1000 of full rated power.
Output device and speakers are guarded by a professional-calibre enrgy-sensing circuit that doesn't limit the low energy, high amplitude short term transients essential to accurate music reproduction. As a result, output signals are free of the distortions and instabilities caused by conventional volt/amp limiting circuitry used in most receivers.

Direct Coupled Power Output
Provides wide power bandwidth, excellent low frequency transient response and improved damping factors. A number of high-power transistorized amplifiers still use capacitor - or transformer-coupled output stages to ensure reliability. However essential this design was in the past, it tended to limit low frequency power response or cause degrading phase shift.
The Marant 2385 achieve their high degree of stability without the need for coupling transformers and capacitors and the sound inaccuracies they can cause. The benefits are extremely high damping factors at low frequencies and excellent low frequency response.

Toroidal Dual Power Supply
A specially designed toroidal-core power transformer wwith dual secondaries gives you two independent power supply sections. Each channel can perform at its best, at all frequencies and levels, without affecting the other channel. In fact, even when one channel is driven by a high level dynamic signal demanding considerable power output, the other can still maintain exceptionally low distortion.
Complementing the transformer are high-capacity dual section electrolytic capacitors. This combination provides high power reserves, reliability and low distortion while keeping heat and weight to a minimum.
Peak Indicators
Both receivers use the same type of sophisticated peak LED display featured in the Marantz Model 510M power amplifier. Rather than simply sense the amp's output voltage as in most LED displays, the unique Marantz circuit tracks variations in the power supply. You get an accurate indication of maximum amplifier output regardless of low or high AC line conditions. Peak indicators, unlike VU meters, react instantaneously to audio transients or excessively high input signals that cause clipping.

Tuner Section
Steep Quieting Slope
The quieting slope specification measures a tuner's ability to provide good Signal-to-Noise performance 
Under actual operating conditions. It's a far more reliable indication of quality than the IHF sensitivity figure often quoted as the prime specification to consider when evaluating an FM tuner.

Highly Sensitive Dual-Gate MOSFET FM Front End
The superior quieting sensitivity of Models 2385 is largely due to the use of a dual-gate MOSFET RF amplifier and mixer stage. Moreover, MOSFET devices deliver extremely linear operation, providing low RF intermodulation distortion and excellent rejection of spurious signals.
An outstanding selectivity specification is ensured by a five-gang tuning capacitor, while a dual-tuned RF interstage provides improved image and spurious signal rejection.

Phase Locked Loop FM Stereo Demodulator
The phase locked loop (PLL) design was developed by the space industry to provide a state-of-the-art. Communication system. Today the same technology is used in all Marantz receivers and tuners to assure low distortion, supoerior noise rejection and excellent stereo separation.
PLL circuitry locks to the stereo pilot signal broadcast by an FM station. This positive "phase lock" enables the multiplex demodulator to separate the stereo channel information from the FM multiplex signal with more accuracy and less distortion than demodulators using other designs.
PLL is dependent on pilot phase and not on pilot aamplitude, making it less susceptible to false triggering from various types of noise interference.

Multi-Stage IF Section
Built into both receivers is a comprehensive six-stage IF amplifier section incorporating five dual-element ceramic filters. The characteristics of these filters produce a 200 kHz passband which is linear in phase, consequently eliminating a major source of high frequency distortion and loss of stereo separation. Sharp cut-off slopes improve tuner selectivity, assuring superior reception even when stations are closely spaced.   A multi-stage limiter comprised of two integrated circuits provides superb AM rejection and an excellent capture ratio - specified at 1 dB. Distortion (at 1 kHz) is kept at a minimal 0,1% in mono, and 0,2% in stereo.

Plug-in Dolby FM Capability
On the back panel of Model 2385 is a convenient receptacle that accepts the optional plug-in Marantz DLB-1 Dolby FM Decoder. Inside the receivers is a 25-microsecond Dolby FM equalization circuit. In tandem, they can cut the noise from a Dolbyized FM broadcast by as much as 12 dB.. That's the equivalent of reducing the noise power of a received FM signal sixteen times below normal.

Additional  Features
The Model 2385 receiver have a multiplex noise filter that reduces the background noise of weak FM stereo signals, while maintaining full frequency response. And they feature adjustable FM muting, a pivoting  AM antenna and an "F" connector for simple connection of coaxial FM antenna cable.

Preamplifier Section
Flexible Tone Controls
The more flexible the the tone controls, the more accurately yoy can adjust for non-linearities caused by speakers, speaker placement, room acoustics or the program material itself.
The tone control system in Marantz Model 2500; 2385 features a sophisticated five-position tone turnover/mode switch for versatile bass, midrange and treble control. This eliminates a major shortcoming of conventional tone controls - their tendency to affect too wide a band of frequencies. Optional frequency turnover points limit the bass and treble controls to just the desired range.
The advantages can be illustrated by a practical example: boosting the low bass (under 100 Hz) to compensate for a deficiency in room acoustics. Most conventional tone controls, even if capable of supplying the boost, will also increase the output in the 300 Hz to 1,000 Hz region.
With the turnover point set at 100 Hz on a Marantz receiver, the bass control can provide the desired bass boost up to the frequency point of 100 Hz and leave the frequency range above the point essentially flat and unaffected.
This flexible, easy-to-set system permits a virtually unlimited number of repeatable settings, enabling you to adjust for the desired tonal balance in any listening environment.

Precision Four-Gang Volume Control
Model 2385 feature a precision-calibrated, stepped volume control. Its superb tracking accuracy of ±0,5 dB between left and right channels enables you to repeat volume settings with total accuracy.
The four-gang design helps produce exceptional Signal-to-Noise performance - typically greater than 10 dB over conventional volume control designs.

Superior Filter Design
The Model 2385 feature an 18 dB per octave Bessel-derived high filter - the most advanced filter design in audio. It reduces high frequency noise - and produces a more natural less colored sound because it eliminates the overshoot and "ringing" common to other filters. Results are linear phase response and greatly reduced phase and transient distortion. An 18 dB/octave 15 Hz subsonic Butterworth low filter cuts turntable rumble and subsonic transients that prevent accurate reproduction of low frequency signals.
Never before has such advanced filter technology been applied to any audio components, separates or receivers. 18 dB/octave filters provide positive filtering action with little coloration of sound by concentrating their effect only at the specified frequencies. Filters with slower roll-off characteristics, on the other hand, must start acting toward the midpoint of the frequency range in order to perform adquately at the extreme high or low end of the audio spectrum.

Flexible Tape Copy Functions
In addition to the standard phono and auxiliary inputs, two sets of tape inputs and outputs are provided to facilitate dubbing between a pair of tape decks. A built-in tape copy facility can function independently of program selector and tape monitor circuitry, enabling you to dub from one deck to another while listening to a different program sourece.
Also featured are front-panel dubbing jacks that allow you to add a third tape deck without disturbing any rear panel connections.
Reat panel facilities include conections for two sets of speaker systems, main in/pre out jack's a Quadradial output jack and two convenience AC outlets.

Amplifier Section
Minimum Continuous Power per Channel (from 20 Hz to 20 kHz, both channels driven): 
Into 8 ohms :  185 W
Into 4 ohms :  240 W
Total Harmonic Distortion
At 8 Ω :  0,05%
At 4 Ω :  0,1%
IM Distortion (IHF method, 60 Hz : 7 kHz = 4:1 at rated power output):
 at 8 Ω :  0,05%
At 4 Ω :  0,1%
Damping Factor (at 20 Hz):  60
Preamplifier Section
Input Overload at 1 kHz :  200 mV
Equivalent Input Noise "A" weighted:  0,48 µV
Dynamic Range:  113 dB
Input Sensitivity at 1 kHz :  1,8 mV / 47 k Ω
Signal-to-Noise Ratio "A" weighted (at rated output & 7,75 mV Input):  83 dB
Frequency response (RIAA, 20 Hz to 20 kHz):  ±0,25 dB
Input Capacitance:  100 pF
High Level Inputs (Aux  & Tape):
Input Sensitivity/Impedance :  180 mV /47 k Ω
Signal-to-Noise  (A weighted):  98 dB
Output Impedance
Tape Out :  500 Ω
Pre out:  50 Ω
AM/FM Tuner Section
IHF Usable [mono]:  8,75 dBf (1,5 µV)
IHF -50 dB Quieting
Mono :  12,1 dBf (2,2 µV)
Stereo :  33,2 dBf (25 µV)
Quieting Slope (mono)
RF input for 30 dB Quieting:  6,8 dBf (1,2 v)
Quieting at:
20 dBf (5,5 µV) :  58 dB
25 dBf (10 µV) :  66 dB
40 dBf (55 µV):  78 db
65 dBf (1,000 µV):  80 dB
Quieting Slope (stereo)
Quieting at:
30 dBf (17 µV) :  49 dB
45 dBf (55 µV) :  62 dB
50 dBf (173 µV):  70 db
65 dBf (1,000 µV):  75 dB
Distortion, Mono and [stereo] at 65 dBf:
At 100 Hz :  0,15% [0,35%]
At 1,000 Hz :  0,1% [0,2%]
At 6,000 Hz :  0,15% [0,3%]
Hum and Noises (at 65 dBf) Mono :  -80 dB
Frequency Response (30 Hz to 15 kHz)
Mono and Stereo :  +0,2 dB -1,0 dB
Capture Raatio:  1 dB
Alternate Channel Selectivity:  85 dB
Spurious Response Rejection:  120 dB
Image response Rejection:  120 dB
IF Rejection(balanced):  120 dB
AM Suppression:  60 dB
Stereo Separation
At 100 Hz :  45 dB
At 1,000 Hz :  50 dB
At 10,000 Hz :  42 dB
Subcarrier rejection:  75 dB
AM Usable Sensitivity (IHF):  10 µV
AM Distortion  at 30% Modulation:  0,4%
AM Signal-to-Noise Ratio:  55 dB
Dimensions (W x H x D):  491 x 178 x 435 mm (19-1/4" x 7" x 17-1/8")
Weight:  27 kg (59,4 lbs)

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